There is widely used a bookshelf-type housing device for housing a plurality of plug-in units (PIUs) arranged in parallel by mounting the PIUs equipped with optical modules, electronic circuits, or the like in connectors on a back wiring board (BWB). This type of housing device is often used in such a way that, for example, as illustrated in FIG. 1, a plurality of housing devices 101 and 101 are stacked in multiple stages in a rack 100 as one functional unit. In the rack 100, the temperature of the housing device 101 arranged in the upper stage rises easily under the influence of exhaust heat from the housing device 101 arranged in the lower stage. In other words, a difference occurs in cooling performance between the housing devices 101 and 101 depending on the arrangement in the rack 100. Although the housing device 101 in each stage is stored so as to occupy the full width of the rack 100 in the example of FIG. 1, a plurality of housing devices each of which is smaller in width than the housing device 101 are placed in one stage of the rack 100 in some cases.
There is known a cooling structure in which a baffle is provided for each housing device 101 to change the flow direction of cooling air which flows from the lower side to the upper side to a flow direction from the lower side to the front or rear side by using the baffle in order to reduce the difference in cooling performance in the rack 100 as described above (for example, refer to Japanese Laid-Open Utility Model Publication No. 56-43976 and Japanese Laid-Open Patent Publication No. 2003-163480). Thereby, for the housing devices 101 stacked in multiple stages, the housing device 101 in the upper stage is not directly subjected to high-temperature exhaust air (subjected to an air blow) from the housing device 101 in the lower stage, thus enabling a reduction in the deterioration of the cooling performance of the housing device 101 in the upper stage. The above baffle is also referred to as “convection inducing plate,” “heat shield plate,” or the like.
FIG. 2 is a perspective view illustrating a configuration example of the conventional housing device with the baffle.
In FIG. 2, the conventional housing device 101 includes a housing 111 made of metal, a baffle section 112 attached so as to cover the upper part of the housing 111, and a BWB 113 put in the backboard portion of the housing 111. In this housing device 101, cooling air taken from an air inlet located in the bottom face is discharged from an air outlet located in the upper part of the rear, as indicated by the arrow lines in FIG. 2.
FIG. 3 is a perspective view of the above conventional housing device 101 from which the top plate of the baffle section 112 is removed to enable checking of the configuration of the upper part of the housing 111 and the inside of the baffle section 112. As illustrated, on the upper part of the housing 111, there are aligned the openings of slots SL1, SL2, SL3, and so forth corresponding to a plurality of PIUs, which are mounted in the connectors on the BWB 113. Each PIU or filler panel is installed in the housing 111, by which each slot SL forms a substantially independent air flow path. The baffle section 112 is hollow. Cooling air (exhaust air) flows discharged from the openings of the slots SLs are mixed in the baffle section 112 and induced to the air outlet.
FIG. 4 is a diagram for describing the flow of the cooling air in the conventional housing device 101. As an example of a specific configuration, this specification describes a case where the housing device 101 has a push-type cooling mechanism provided with a fan unit 114 in the lower part of the housing 111 and includes a slot region 115 in which full-size PIUs are mountable and slot regions 115U and 115L in which half-size PIUs are mountable in the upper and lower two or more stages.
With fan motors 114F1 to 114F3 and 114B1 to 114B3 provided in the fan unit 114 being driven, the cooling air taken from the air inlet located in the bottom face passes through the fan unit 114 and an air plenum section 116 and is induced into the slots in the slot region 115 corresponding to the full-size PIUs and the slots in the lower-stage slot region 115L out of the slot regions 115U and 115L corresponding to the half-size PIUs, as indicated by the thick arrow lines illustrated in the side view in the upper right of FIG. 4. The cooling air, having flown from the lower side to the upper side within each slot in the slot region 115, is released into the baffle section 112. Moreover, the cooling air, having flown from the lower side to the upper side in each slot in the lower-stage slot region 115L, flows from the lower side to the upper side in the upper-stage slot region 115U in the same slot and is released into the baffle section 112. Thereafter, in the baffle section 112, the cooling air flows, having passed through the slots, are mixed with one another, and the flow of the cooling air is directed to the rear by the top plate of the baffle section 112 and then discharged to the outside from the air outlet located in the upper part of the rear.
Now, closely observing the flow of the cooling air released from the adjacent slots into the baffle section 112 in the conventional housing device as described above, the cooling air released from the slots SL1 to SL3 to the baffle section 112 smoothly flows in the baffle section 112 without mutual interference and are discharged from the air outlet to the outside as long as the same amount of air (pressure) passes through each of the adjacent slots SL1, SL2, and SL3 as illustrated in FIG. 5, in which region “a” enclosed by an alternate long and short dash line of the above FIG. 4 is enlarged.
As a practical matter, however, the same amount of air rarely passes through each of the adjacent slots SL1 to SL3 due to structural factors of the housing device, and a difference occurs in the amount of passing air depending on the slot. In other words, the conventional housing device has slot dependence in the amount of passing air.
As one of the structural factors of the housing device, there is a positional relation between the slots and the fan motors. Specifically, the amount of airflow produced by individual fan motors is low in the vicinity of the axis of rotation of the fan and high in the vicinity of the blades of the fan. In addition, a difference occurs in the amount of airflow due to individual variation of the fan motors. Therefore, in the above configuration example illustrated in FIG. 4, a difference occurs in the amount of passing air depending on the positions of the slots relative to the six fan motors 114F1 to 114F3 and 114B1 to 114B3 in the fan unit 114.
Moreover, another structural factor is a difference that occurs in whether air flows well depending on the slot according to the internal shape of the housing device, in other words, a difference in airflow resistance among the slots. For example, in the configuration of the above FIG. 4, the slot in which the half-size PIU is mountable includes many structural objects such as a rail for guiding the PIU to a predetermined position in comparison with the slot in which the full-size PIU is mountable, and therefore the airflow resistance is relatively high in the slot for the half-size PIU. Further, a difference occurs in the airflow resistance also depending on whether the PIUs are mounted in the slots or according to the structure of the PIU to be mounted.
If the slot dependence exists in the amount of passing air as described above, turbulence occurs in the flow of the cooling air in the baffle section 112. FIG. 6 specifically illustrates this situation. Similarly to FIG. 5 in the above, the arrow lines in FIG. 6 indicate the flows of cooling air and a difference in thickness of the arrow line indicates a difference in the amount of passing air (pressure). In this specification, the amount of air passing through the slot SL2 is less than the amount of air passing through each of the adjacent slots SL1 and SL3. The cooling air, having passed through each of the slots SL1 to SL3, is forcibly changed in the direction by the top plate of the baffle section 112. At this time, the cooling air from the slots SL1 and SL3 through each of which more amount of air passes (higher in pressure) flows into the region on the slot SL2 side where less amount of air flows (lower in pressure), thereby obstructing the flow of cooling air from the slot SL2 to the baffle section 112. The turbulence of the cooling air in the baffle section 112 further increases the slot dependence in the amount of passing air which is caused by the structural factors of the housing device. This is likely to notably decrease the amount of air passing through the slot SL2 and to reduce the cooling capacity problematically.
Moreover, the effect of the turbulence of the cooling air in the baffle section as described above is more obvious when a large bias occurs in the amount air passing through each slot such as in the case of a trouble or replacement of any of the fan motors or replacement of any of the PIUs. The limit in cooling performance of the housing device depends on the slot through which the least amount of air passes among the plurality of slots. Therefore, the higher the slot dependence in the amount of passing air, the lower the cooling performance of the entire housing device. This makes it difficult to design the device. Moreover, the amount of air passing through the corresponding slot notably decreases at the time of replacement of the fan motor or PIU, and therefore the time allowed for the replacement is limited to a shorter period of time.